This invention relates to a scroll-type fluid machine having an improved journal bearing for the shaft of one of the scrolls. More particularly but not exclusively, it relates to a scroll-type vacuum pump of the type having two rotating scrolls.
A scroll-type fluid machine is a positive displacement machine having two interfitting elements usually referred to as scrolls. Each scroll includes a disk-shaped end plate and a thin-walled member, referred to as a spiral wrap, which projects perpendicularly from one surface of the end plate and curves outwards from the center of the end plate in the shape of an involute or other type of spiral. The two scrolls are disposed with the end plates parallel and the spiral wraps interfitting with one another so that they are in line contact at a plurality of locations. The surfaces of the end plates and the spiral wraps define a plurality of spiral compression chambers between the points of contact between the spiral wraps. If the scrolls are rotated with respect to one another in the proper direction while maintaining the line contact between the spiral wraps, the compression chambers are gradually moved towards the centers of the scrolls with an accompanying decrease in volume. A working fluid is introduced into the compression chambers via a suction port formed in the outer periphery of one of the scrolls and is then removed at a higher pressure from a discharge port formed in the center of the end plate of one of the scrolls.
Each of the scrolls is equipped with a shaft by means of which the scroll is rotatably supported. The shafts are supported by journal bearings secured to casings which enclose the scrolls. However, because the bearings are secured to the casings, it is difficult to disassemble the scrolls of a conventional scroll-type fluid machine when the machine needs to be repaired. It is also difficult to adjust the positions of the bearings.